1. Field of the Invention
The present invention relates to separating a pane of a brittle material from a moving ribbon of the material, and in one configuration, to separating panes of glass from a moving ribbon of glass, while reducing the introduction of disturbances into the upstream ribbon.
2. Description of Related Art
Specialized glasses have found increased applicability, including substrates, in the manufacture of display devices. For example, liquid crystal displays (LCDs) have become increasingly popular for displaying information in calculators, watches, video games, audio and video equipment, portable computers and even car dashboards. The improving quality and size of LCDs has made the LCDs an attractive alternative to cathode ray tubes (CRTs) which are traditionally used in television sets and desktop computer displays. In addition, other flat panel display (FPD) types, such as plasma displays (PDs), field emission displays (FEDs) and organic light-emitting polymer displays (OLEDs) are being developed as alternatives to LCDs. Thin film transistor liquid crystal displays (TFT-LCD) are used in notebook computers, flat panel desktop monitors, LCD televisions, and Internet and communication devices, to name only a few. It is increasingly useful to incorporate electronic components onto a glass sheet (glass substrate) used in the display device. Some display devices such as TFT-LCD panels and OLED panels are made directly on flat glass sheets. For example, the transistors are arranged in a patterned array and are driven by peripheral circuitry to provide (switch on) desired voltages to orient the molecules of the LC material in the desired manner.
In-plane stress (and resulting strain) can result in a variation of the alignment of the transistors and the pixels. This can result in distortion in the display panel. As such, in LCD and other glass display applications, it is exceedingly beneficial to provide glass (substrates) that are within acceptable tolerances for distortion.
Flat panel display manufacturers are finding that demands for larger display sizes and the economies of scale are driving manufacturing processes to larger size pieces of glass. Industry standards have evolved from Gen III (550 mm×650 mm), Gen III.5 (600 mm×720 mm), and Gen IV (1,000 mm×1,000 mm) sizes and larger. As the desired size of the glass pieces increases, the difficulty of the production and handling increases.
The manufacturing of the glass used as the substrate is extremely complex. The drawdown sheet or fusion process, described in U.S. Pat. No. 3,33 8,696 (Dockerty) and U.S. Pat. No. 3,682,609 (Dockerty), herein incorporated by reference, is one of the few processes capable of delivering the glass without requiring costly post forming finishing operations such as lapping and polishing.
However, the fusion process requires the separation and removal of panes from a continuously moving ribbon of glass. Traditionally, the separation of the panes has been performed by forming a separation line in the ribbon of glass. Then a vacuum cup array is attached to the glass below the score line and the portion of the ribbon below the score line is rotated less than 15° to cause the glass to break at the score line and thus form the desired glass pane. This breaking produces a newly formed leading edge on the moving ribbon and a newly formed trailing edge on the glass pane.
However, this exertion of such a large bending moment on the ribbon, imparts significant potential energy to the ribbon, particularly upon the snapping of the pane from the ribbon. Introduction of this energy (and mechanical disturbance) into the upstream ribbon can lead to undesirable characteristics in subsequent glass panes.
Therefore, there is a need to provide for the separation of a pane from a continuously moving ribbon of brittle material, while reducing imparted disturbances which can propagate upstream along the ribbon. The need also exists for increasing control over the crack propagation used to separate a pane from the ribbon.